Television receiver with isolated inputs

ABSTRACT

Receivers ( 1 ) comprising television and radio inputs ( 11,12 ) for receiving television and radio signals and comprising switching circuits ( 2 ) with two first switches ( 21,22 ) to be activated in a first mode and located parallelly to the television input ( 11 ) and with two second switches ( 23,24 ) to be activated in a second mode and located anti-serially to the radio input ( 12 ), and control circuits ( 3 ) for controlling the switching circuits ( 2 ) are modified in such a way that strong radio signals can no longer disturb the television signals. Thereby one of the first switches ( 21 ) and one of the second switches ( 23 ) together isolate the inputs ( 11,12 ) from each other, and the control circuit ( 3 ) supplies a first control signal to the first switches ( 21,22 ) and supplies a second control signal to non-common points of the anti-serial second switches ( 23,24 ). This kind of receivers ( 1 ) no longer need different switching circuits ( 2 ) for shielded radio inputs and unshielded radio inputs. The switches ( 21,22,23,24 ) are diodes, and the control circuit ( 3 ) comprises transistors ( 31,32 ) for controlling the diodes.

The invention relates to a receiver comprising a first input forreceiving a first signal and comprising a second input for receiving asecond signal and comprising a switching circuit with at least two firstswitches to be activated in a first mode and with at least two secondswitches to be activated in a second mode and comprising a controlcircuit for controlling the switching circuit.

The invention also relates to a switching circuit and a control circuitfor use in such a receiver, to a television comprising such a receiver,and to a method comprising the steps of at a first input receiving afirst signal and at a second input receiving a second signal, activatingat least two first switches in a first mode, and activating at least twosecond switches in a second mode, and controlling the switching.

Such a receiver is for example a television receiver having the first(shielded) input to be coupled to for example a satellite disk or acable or a television antenna for receiving first signals like forexample television signals and having the second (shielded orunshielded) input to be coupled to for example a radio antenna (when forexample shielded) or a wire (when for example unshielded) for receivingsecond signals like for example Frequency Modulated radio signals or FMradio signals. Generally, the first switches are located parallelly tothe first input and are activated (made conducting) in a first(television) mode and the second switches are located anti-serially tothe second input and are activated (made conducting) in a second (radio)mode, for example.

A prior art receiver is known from U.S. Pat. No. 6,020,936, whichdiscloses in its second figure a TVIN (the first input) and a FMIN(second input) coupled to each other via four diodes D1-D4 (switches) ofwhich in a TV mode D1 and D3 are conducting and D2 and D4 are not and ina FM mode D2 and D4 are conducting and D1 and D3 are not. Thisconducting and non-conducting is controlled by a control circuitgenerating the TV/FM signal (control signal). In view of TVIN, D1 and D3are located parallelly, and in view of FMIN, D2 and D4 are locatedanti-serially.

The known receiver is disadvantageous, inter alia, due to strong secondsignals (strong FM signals) arriving via the second input (FMFN)disturbing the first signals (TV signals).

It is an object of the invention, inter alia, of providing a receiver asdefined in the preamble in which there is a reduced disturbance of anyfirst signals by strong second signals. The invention is defined by theindependent claims. The dependent claims define advantageousembodiments.

By isolating the inputs from each other via at least two switches,compared to the prior art U.S. Pat. No. 6,020,936 where there is acoupling via just one switch D1 (plus one or more other elements)between the inputs, the inputs in the receiver according to theinvention are much better isolated from each other. Even strong secondsignals can no longer disturb any first signals. Due to this betterisolation, the first switches and the second switches now require(separated) first control signals and second control signals. Whensupplying the second control signal to (non-common points of) the(anti-serial) second switches, one of the first switches can be coupledadvantageously to the common point of these (anti-serial) secondswitches.

The invention is based upon an insight, inter alia, that more switchesin a coupling will bring more isolation, and is based upon a basic idea,inter alia, that one of the first switches should be shifted from (priorart) the non-common point of the anti-serial second switches—whichnon-common point is coupled to the second input—to (invention) thecommon point of these anti-serial second switches.

The invention solves the problem, inter alia, of providing a receiver asdefined in the preamble which better isolates the inputs from eachother, and is advantageous, inter alia, in that this kind of receiversno longer need different switching circuits for shielded second inputsand unshielded second inputs.

A first embodiment of the receiver according to the invention as definedin claim 2 is advantageous in that the first switches are diodes ofwhich the anodes are coupled to the first input via one or moreelements, with the second switches being diodes of which the cathodesform a common point. By supplying the first control signal to the anodesof the first switches and supplying the second control signal to theanodes of the second switches, the prior art inverter can be avoided.The diodes are advantageous low cost switches.

A second embodiment of the receiver according to the invention asdefined in claim 3 is advantageous in that the cathode of the one of thefirst switches is coupled to the common point and that the cathode ofthe other one of the first switches is coupled to a filter-input via oneor more elements, with an anode of one of the second switches beingcoupled to the second input via one or more elements and with an anodeof the other one of the second switches being coupled to thefilter-input via one or more elements. The elements for example comprisecapacitors, inductors, resistors etc. for filtering purposes.

A third embodiment of the receiver according to the invention as definedin claim 4 is advantageous in that the receiver comprises a low bandfilter comprising the filter-input for low band filtering televisionsignals and radio signals. The low band filter is then used for bothkinds of signals, which is advantageous. Usually, there will be morefilters, like a medium band filter and a high band filter, coupled tothe first input via one or more elements for medium band filtering andhigh band filtering television signals.

A fourth embodiment of the receiver according to the invention asdefined in claim 5 is advantageous in that the control circuit comprisesa third switch of which a first contact is coupled to a common point ofa first serial circuit of two resistors of which the non-common pointsare coupled to the anodes of the first switches, with the controlcircuit further comprising a fourth switch of which a first contact iscoupled to a second contact of the first transistor and to a commonpoint of a second serial circuit of two resistors of which thenon-common points are coupled to the anodes of the second switches, withthe common point of the second switches being coupled to ground via aresistor. This control circuit is an advantageous low cost, low complexcontrol circuit. The resistor between the common point and ground allowsboth second switches to be biased reversibly for improvednon-conduction.

A fifth embodiment of the receiver according to the invention as definedin claim 6 is advantageous in that the third switch comprises a firsttransistor and the fourth switch comprises a second transistor, withfirst contacts of the transistors being collectors, with second contactsof the transistors being bases, and with emitters of the transistorsbeing coupled to ground, with the collectors each via at least oneresistor being coupled to a first voltage source and with the basis ofthe first transistor being coupled to the collector of the secondtransistor via a resistor and with a basis of the second transistorbeing coupled to a second voltage source via at least one resistor. Thiscontrol circuit generates the first control signal and the secondcontrol signal dependently upon the voltage sources and can therefore becontrolled easily. The transistors are advantageous low cost switches.

Embodiments of the switching circuit according to the invention, of thecontrol circuit according to the invention, of the television accordingto the invention and of the method according to the invention correspondwith the embodiments of the receiver according to the invention.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments(s) described hereinafter.

The sole FIGURE illustrates in block diagram form an embodiment of areceiver according to the invention comprising a switching circuitaccording to the invention and a control circuit according to theinvention.

The receiver 1 according to the invention comprises a switching circuit2 according to the invention and a control circuit 3 according to theinvention.

Switching circuit 2 comprises two first switches 21,22 like for examplediodes and two second switches 23,24 like for example diodes. An anodeof diode 21 is coupled to ground via an element 65 for examplecomprising a capacitor and to a first non-common point of a first serialcircuit 61,62 comprising resistors 61 and 62, of which a secondnon-common point is coupled to an anode of diode 22 and to a high bandfilter 16 and to a first input 11 via an element 13 for examplecomprising a capacitor. First input 11 is further coupled to a mediumband filter 15.

A cathode of diode 22 is coupled via an element 66 for examplecomprising a capacitor to a filter-input of a low band filter 17 and toan element 67 for example comprising a capacitor, which is furthercoupled to an anode of diode 24. A cathode of diode 24 is coupled to acathode of diode 21 and to a cathode of diode 23 and is coupled toground via a resistor 63 and to the cathode of diode 22 via a resistor64. An anode of diode 23 is coupled to a second input 12 via an element14 for example comprising a capacitor.

Control circuit 3 comprises a third switch 31 for example in the form ofa first transistor 31 (npn) of which an emitter is coupled to ground andof which a collector (first contact) is coupled to a common point of thefirst serial circuit 61,62 and via resistors 73,76 to a first voltagesource 77,78. A basis (second contact) of first transistor 31 is coupledvia a resistor 75 to a common point of a second serial circuit 71,72comprising resistors 71 and 72, of which a first non-common point iscoupled to the anode of diode 23 and of which a second non-common pointis coupled to the anode of diode 24. Control circuit 3 further comprisesa fourth switch 32 for example in the form of a second transistor 32(npn).

The common point of the second serial circuit 71,72 is further coupledto a collector (first contact) of the second transistor 32 (npn) and viaa resistor 74 and via the resistor 76 to the first voltage source 77,78.An emitter of second transistor 32 is coupled to ground, and a basis(second contact) is coupled via a resistor 79 to a second voltage source80,81. Both voltage sources 77,78 and 80,81 comprise an internalresistance 77,80 and a source 78,81.

Receiver 1 functions as follows. In a first mode like for example atelevision mode, for example the first voltage source 77,78 is switchedon and the second voltage source 80,81 is switched on. As a result,first transistor 31 is non-conductive, second transistor 32 isconductive, first diodes 21,22 are conductive and second diodes 23,24are non-conductive, and first signals like for example televisionsignals arriving at first input 11 flow to medium band filter 15 and viaelement 13 to high band filter 16 and via element 13 and diode 22 andelement 66 to low band filter 17. Second signals like for exampleFrequency Modulated radio signals arriving at second input 12 areblocked by non-conductive diodes 23,24.

In a second mode like for example a radio mode, for example the firstvoltage source 77,78 is switched on and the second voltage source 80,81is switched off. As a result, first transistor 31 is conductive, secondtransistor 32 is non-conductive, first diodes 21,22 are non-conductiveand second diodes 23,24 are conductive, and first signals like forexample television signals arriving at first input 11 are blocked bynon-conductive diode 22. Second signals like for example FrequencyModulated radio signals arriving at second input 12 now flow via element14 and conductive diodes 23,24 and element 67 to low band filter 17.

For both modes, one low band filter 17 can be advantageously used forboth inputs 11,12. By isolating the inputs 11,12 from each other via atleast two diodes 23,21, compared to the prior art U.S. Pat. No.6,020,936 where there is a coupling via just one diode 21 (plus one ormore other elements) between the inputs 11,12, with diode 21 accordingto this prior art not being coupled to the cathode of diode 23 but tothe anode of diode 23, the inputs 11,12 in the receiver 1 according tothe invention are much better isolated from each other. Even strongsecond signals like strong radio signals can no longer disturb any firstsignals like television signals. Due to this better isolation, the firstdiodes 21,22 and the second diodes 23,24 now require (separated) firstcontrol signals arriving via the first serial circuit of resistors 61,62and second control signals arriving via the second serial circuit ofresistors 71,72. When supplying the second control signal to non-commonpoints of the anti-serial second diodes 23,24, one of the first diodes21 can be coupled advantageously to the common point of theseanti-serial second diodes 23,24.

In the first mode, the resistor 63 forms a voltage divider together withresistors 62 and 73 for the first voltage source 77,78 and therebyallows both second diodes 23,24 to be biased reversibly for improvednon-conduction (the voltage at the anodes of these first diodes can thenbe lower than the voltage at their cathodes). As a result,intermodulation products due to non-linearities of switching diodes areavoided.

The invention is based upon an insight, inter alia, that more switchesin a coupling will bring more isolation, and is based upon a basic idea,inter alia, that one of the first switches 21,22 should be shifted from(prior art) the non-common point of the anti-serial second switches23,24—which non-common point is coupled to the second input 12—to(invention) the common point of these anti-serial second switches 23,24.

The invention solves the problem, inter alia, of providing a receiver 1which better isolates the inputs 11,12 from each other, and isadvantageous, inter alia, in that this kind of receivers 1 no longerneed different switching circuits 2 for shielded second inputs 12 andunshielded second inputs 12.

The switches 21-24 can be diodes or can be transistors etc. Thetransistors 31 and 32 can be npn transistors or pnp transistors or FETsor MOSFETs etc. and can comprise other embodiments of general switches.The elements can be much more complex and other elements are not to beexcluded and certain elements may be combined and/or deleted (like forexample either resistor 76 or resistors 73,74), and further inputsand/or further filters and/or further modes are not to be excluded, thisall without departing from the scope of this invention.

For example serially to each filter 15-17 there may be an inductor.Between input 11 and element 13 there may be for example an elementgroup of a capacitor Ca of which both sides are coupled to ground eachvia an inductor La,Lb, with a parallel circuit of a capacitor Cb and aninductor Lc being coupled serially to the capacitor Ca. Instead ofelement 14 being coupled to resistor 71 and the anode of diode 23, theremay be for example an element group of a parallel circuit of a capacitorCx and an inductor Lx coupled to the input 12 and via a capacitor Cw tothe anode of the diode 23, with both sides of the capacitor Cy beingcoupled to ground, a first side (which is coupled to the parallelcircuit) via an inductor Ly and a second side (which is coupled to theanode) via a serial circuit of an inductor Lz and a capacitor Cz, ofwhich serial circuit the common point is then coupled to the resistor71. And serially to low band filter 17, there may be for example aparallel circuit of a capacitor and a resistor.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.The word “comprising” does not exclude the presence of elements or stepsother than those listed in a claim. The word “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention can be implemented by means of hardware comprising severaldistinct elements, and by means of a suitably programmed computer. Inthe device claim enumerating several means, several of these means canbe embodied by one and the same item of hardware. The mere fact thatcertain measures are recited in mutually different dependent claims doesnot indicate that a combination of these measures cannot be used toadvantage.

1. Receiver comprising: a first input for receiving a first signal; asecond input for receiving a second signal; a switching circuit with atleast two first switches to be activated in a first mode and with atleast two second switches to be activated in a second mode; and acontrol circuit for controlling the switching circuit, characterized inthat at least one of the first switches and at least one of the secondswitches together isolate at least one of the inputs from the other,with the control circuit supplying a first control signal to the firstswitches and supplying a second control signal to the second switches.2. Receiver according to claim 1, characterized in that the firstswitches are diodes of which the anodes are coupled to the first inputvia one or more elements, with the second switches being diodes of whichthe cathodes form a common point.
 3. Receiver according to claim 2,characterized in that the cathode of the one of the first switches iscoupled to the common point and that the cathode of the other one of thefirst switches is coupled to a filter-input via one or more elements,with an anode of one of the second switches being coupled to the secondinput via one or more elements and with an anode of the other one of thesecond switches being coupled to the filter-input via one or moreelements.
 4. Receiver according to claim 3, characterized in that thereceiver comprises a low band filter comprising the filter-input for lowband filtering television signals and radio signals.
 5. Receiveraccording to claim 4, characterized in that the control circuitcomprises a third switch of which a first contact is coupled to a commonpoint of a first serial circuit of two resistors of which the non-commonpoints are coupled to the anodes of the first switches, with the controlcircuit further comprising a fourth switch of which a first contact iscoupled to a second contact of the third switch and to a common point ofa second serial circuit of two resistors of which the non-common pointsare coupled to the anodes of the second switches, with the common pointof the second switches being coupled to ground via a resistor. 6.Receiver according to claim 5, characterized in that the third switchcomprises a first transistor and the fourth switch comprises a secondtransistor, with first contacts of the transistors being collectors,with second contacts of the transistors being bases, and with emittersof the transistors being coupled to ground, with the collectors each viaat least one resistor being coupled to a first voltage source and withthe basis of the first transistor being coupled to the collector of thesecond transistor via a resistor and with a basis of the secondtransistor being coupled to a second voltage source via at least oneresistor.
 7. Switching circuit for use in a receiver comprising a firstinput for receiving a first signal, a second input for receiving asecond signal, and the switching circuit with at least two firstswitches to be activated in a first mode and with at least two secondswitches to be activated in a second mode, characterized in that atleast one of the first switches and at least one of the second switchestogether isolate at least one of the inputs from the other.
 8. Controlcircuit for use in a receiver comprising a first input for receiving afirst signal, a second input for receiving a second signal, a switchingcircuit with at least two first switches to be activated in a first modeand with at least two second switches to be activated in a second mode,and the control circuit for controlling the switching circuit,characterized in that at least one of the first switches and at leastone of the second switches together isolate at least one of the inputsfrom the other, with the control circuit supplying a first controlsignal to the first switches and supplying a second control signal tothe second switches.
 9. Television comprising a receiver comprising afirst input for receiving a first signal and comprising a second inputfor receiving a second signal and comprising a switching circuit with atleast two first switches to be activated in a first mode and with atleast two second switches to be activated in a second mode andcomprising a control circuit for controlling the switching circuit,characterized in that at least one of the first switches and at leastone of the second switches together isolate at least one of the inputsfrom the other, with the control circuit supplying a first controlsignal to the first switches and supplying a second control signal tothe second switches.
 10. Method comprising the steps of: at a firstinput receiving a first signal; at a second input receiving a secondsignal; activating at least two first switches in a first mode;activating at least two second switches in a second mode; andcontrolling the switching, characterized in that at least one of thefirst switches and at least one of the second switches together isolateat least one of the inputs from the other, with the step of controllingcomprising the steps of supplying a first control signal to the firstswitches and of supplying a second control signal to the secondswitches.